Multi-Input Multi-Output (MIMO) technology is to improve efficiency in data transmission and reception by using multiple transmitting antennas and multiple receiving antennas instead of a single transmitting antenna and a single receiving antenna. If a single antenna is used, a receiver receives data through a single antenna path. However, if multiple antennas are used, the receiver receives data through various paths. Accordingly, speed and amount in data transmission may be increased, and coverage may be increased.
As information fed back from a receiver (for example, user equipment) to a transmitter (for example, base station) in a multi-antenna wireless communication system, a rank indicator (RI), precoding matrix index (PMI), and channel quality information (CQI) are defined. This feedback information may be referred to as channel status information (CSI). The user equipment may feed its desired PMI and RI back to the base station on the basis of a result of channel measurement from the base station. In this case, if the RI desired by the user equipment is used by the base station in a given channel status, it corresponds to a downlink transmission rank value that may have the highest transmission rate. Also, the PMI desired by the user equipment is an index representing a precoding matrix suitable for a channel status measured by the user equipment, in a codebook which is a set of precoding matrix candidates. The codebook is previously determined and shared between the base station and the user equipment. Also, the CQI is calculated on the basis of PMI/RI reported by the user equipment, and corresponds to a modulation and coding scheme (MCS) level applied to downlink transmission. In this case, if precoder information and rank value based on the PMI/RI reported by the user equipment are used, the CQI may represent MCS level that provides an allowable packet error rate.